Detecting the source of water production remains a major challenge during evaluation of fractured carbonate reservoirs. In heterogeneous formations, when the horizontal section passes through a fracture or set of fractures, improper drawdown can allow formation water to flow through these conduits, increasing water cut and blocking hydrocarbon production.

On the contrary, in cases of horizontal wells with three phases of fluid flow, the presence of inflow control devices (ICDs), sliding slide doors (SSDs), slotted liners, and swell packers can add to the complexity of the logging environment and exasperate the ability to accurately quantify production using a production logging tool (PLT).

Using horizontal production logging alone can help identify the point of water entry; yet, in cases of slotted liners, it can be difficult to pinpoint the source of water and the direction of flow. The use of oxygen activation can help identify water movement inside or behind liners and confirm the direction of flow. The integration of both techniques helps minimize uncertainty and enhance interpretation.

This paper discusses a case study from Pertamina Hulu Energi-West Madura Offshore (PHE-WMO). The difficulties associated with identifying water sources in horizontal wells drilled in complex carbonate reservoirs completed with ICDs, SSDs, and swell packers are discussed. It documents a well with high water cut, making water point identification more challenging. Also, it discusses the advantages of using a spectral flow log with a horizontal PLT, versus using the latter only.

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